The complete absence of transfer RNA genes in the mitochondrial genome (maxicircle and minicircle DNA),, is one of the unique features characterizing kinetoplastid organisms. Our previous gel electrophoresis, amino acylation,l and hybridization studies have shown that, the mitochondrion isolated from Leishmania tarantulae is free of cytoplasmic contaminants but contains functional tRNAs, most f which appear to be identical with cytoplasmic tRNAs {e.g.,tRNAleu], while some other are unique [tRNAmet and possibly tRNAtrp]. It is suggested that most if not all mitochondrial tRNAs are nuclear-DNA encoded and possibly imported, but this must be confirmed by direct sequencing and cloning analyses. The immediate goal of this research, therefore, is to obtain direct evidence that specific mitochondrial tRNAs are of nuclear origin. This goal can be attained if a nuclear gene clone having the same sequence as the mitochondrial tRNA sequence in question is found. In this research, therefore, all isoacceptor forms of mitochondrial and cytoplasmic tRNAs for leucine,l methionine and tryptophan will be identified, gel-purified, and sequenced, their modified bases determined, and the nuclear gene cloning and sequencing conducted. The presence of the mitochondrial tRNA sequence in the nucleus will also rule out the possibility that these mitochondrial tRNAs are created by RNA editing from maxicircle or minicircle transcripts. The information gained from these studies should provide necessary groundwork for defining the mechanisms of tRNA import and the nuclear gene regulation of mitochondrial function as part of developmental control occurring in these parasitic organisms.